US2863900A - Synthesis of organic phosphorus compounds - Google Patents

Description

2,863,900 Patented Dec. 9, 1958 SYNTHESIS @lF ORGANIC PHOSPHORUS COMPUUNDS Leland K. Beach, Mountainside, and Robert Drogin, Linden, N. 1., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application April 8, 1953 Serial No. 347,622

Claims. (Cl. 260-461) This invention relates to the manufacture of organic intermediates and more particularly to the production of alkyl phosphonic acid derivatives which are useful in the synthesis of organic phosphorus compounds.

The phosphonic acid derivatives which are of interest have the general structure:

where R is a radical such as methyl, phenyl, or such organic group and where X and Y may be hydroxyl, organic groups such as methoxyl or another phosphorus compound such as:

i i CHa-POPCH3 or where X or Y may be other negative groups.

A more specific object of this invention is the production of methane phosphonic acid derivatives from dimethyl hydrogen phosphite (DMHP) by means of a catalytic rearrangement.

Specifically this invention involves the newly discovered improvement in the thermal rearrangement of DMHP brought about by the use of BP a boron fluoride complex type catalyst, or an equivalent catalyst described as a BB, type catalyst.

The preparation of alkyl phosphonic acid derivatives commonly involves treating a trialkyl phosphite with a primary alkyl halide such as methyl iodide;

(RO)3P OHBI (ROhfi CH3 RI This is called the Arbusov reaction. Although this reaction is almost 100% efiicient and very rapid at moderate temperatures it is expensive due both to the use and recovery of the iodide and also to the use of 'trialkyl phosphite.

For example, trimethyl phosphite is made by reacting three moles of methanol with one mole of phosphorus trichloride in the presence of at least three moles of a base such as diethylaniline. The reaction is expressed as follows:

The use of the base is a large item of expense. The yields with the base are frequently below 50%, and the operation is difficult, involving filtration and removal of large quantities of solvent.

On the other hand DMHP can be made from methanol and PCl without the use of base according to the equation:

3CH OH+PC1 (CH O) PHO+2HCl-l-CH Cl The yields by this process are much higher than those for trimethyl phosphite. The operation is relatively simple.

The complete thermal rearrangement of DMHP gives roughly mole percent yields of various methane phosphonic acid derivatives having the structure,

i CHaPO-- I l in common. This step is considerably less efiicient than the last step of the alternate synthesis from the trialkyl phosphite via the Arbusov reaction. It also requires higher temperatures, longer times, ,and involves the handling of very corrosive material.

There is considerable incentive for obtaining yields above the 75% given by the thermal rearrangement.

As a result of studies of this thermal rearrangement, there have been investigated for catalytic activity many compounds, such as AlCl toluene sulfonic acid pyromethane phosphonic acid, sodium methoxide, methyl sulfate, sulfuric acid, pyridine and others. Of the catalysts studied, those most closely related to BF or its complexes, were found to be unusually beneficial.

In the process of the present invention, the use of less than 10 wt. percent, preferably less than 1 wt. percent of BF allows the DMHP rearrangement reaction to be carried out at lower temperatures, with less corrosion, and with higher yields of the desired products.

BP has been discovered, in accordance with the present invention, to catalyze especially the reaction:

2DMHP DMMP Mono This reaction produces no phosphates. One mode of operation is to carry the reaction no farther than to that point at which secondary reactions adversely affect the yield. The partially converted mixture is then treated to separate out pure DMMP which has the desired structure. The unconverted DMHP may be recycled. product, monomethyl phosphite, may be'converte'd back to DMHP.

Phosphates, formed by secondary reactions are undesirable because they are difiicult to remove. If not removed they produce undesirable phosphate impurities when the methane phosphonic acid derivatives are further processed. In addition to this role' asimpurities, their presence indicates a loss in yield of the desired methane phosphonic structure. v

An alternate more simple mode of operation involves pyrolyzing the BF -DMHP starting mixture at an elevated temperature, such as 160-200 C., to about phosphite conversion and then finishing up at a still higher temperature, such as 225 C. Although some undesirable products, especially phosphates, are formed by this mode of operation their amount are much lower than if no BB, were used. These and other facts are made more clear by the following examples.

Example 1.--Thermal Z-stage rearrangement with no BF catalyst DMHP was heated 42 hours at 181 C. and then 1 hour at 250 C. The resulting product contained 0.2 mole percent of total phosphorus in the form of unconverted phosphite and 12% in the form of phosphates.

Example 2.2stage rearrangement with BF catalyst a,eea,900

Example 3.Reactt'on rate-Without BF catalyst DMHP was heated 4 hours at 160 C. at which time only 9% DMHP and 4% of total phosphite were converted to other products. About 0.1 mole percent phosphate was formed along with about 5 mole percent each of mono methyl phosphite and dimethyl methane phosphonate.

Example 4.--Reacti01z rate--Witlt BF catalyst DMHP containing 1.2 mole percent (0.7 wt. percent) BF was heated 38 minutes at 160 C. At this time 32% of DMHP and 16% of total phosphite were converted. Only about 0.025 mole percent phosphate was formed along with about 17% of mono methyl phosphite and 13% of dimethyl methane phosphonate.

Example 5.Reacti0n rate-With 131 catalyst Example 4 was continued to 4 hours at which time 52% of the DMHP and 28% of total phosphite had been converted. At that time only 0.8 mole percent phosphate had been formed along with 27 mole percent of methane phosphonic acid derivatives.

Example 6.-One stage-High temperature without 8P Crude DMHP was completely pyrolyzed at a temperature up to about 240 C. max. The final product contaiaed about 77 mole percent of methane phosphonic acid derivatives and about 17 mole percent phosphates.

Example 7.One stage-Higlz temperature with BF Crude DMHP containing 0.9 wt. percent BF was completely pyrolyzed over a 3.7 hour period by refluxing to a maximum temperature of about 240 C. The product contained about 85% of the desired methane phosphonic acid derivatives and about 11 mole percent phosphates.

Examples 1-5 above show how B1 increases tremendously the initial rate of pyrolysis giving also less of the undesirable phos hate as by-product at any given conversion level. Examples 6 and 7 show how at complete phosphite conversion the use of less than 1% E1 results in an approximately 8% increase in yield of desired prod- Besides the batch method of pyrolysis there are the two or three stage methods, continuous methods, and others which may be used with benefits of the BF type catalyst.

It is seen from the examples that a desirable mode of operation is a relatively low temperature (below about 200 C.) soaking of DMHP in the presence of B1 in a batch or continuous operation followed by a higher temperature batch, continuous batch or continuous operation to arrive at closer to complete conversion of the phosphite. This may involve simply heating a batch at two different temperatures or may involve a simple continuous feed to a series of enclosed cascading or connected batch reactors or it may involve a continuous coil operation. rivatives produced may be recirculated back to an initial stage to be mixed with the BF catalyst and the phosphite feed. The phosphite feed may have been previously partially converted in the presence of B1 The temperature for the first stage is usually below In such an operation the phosphonic acid de- 200 C. and in the second stage is usually above 220 C. The times of reaction vary with the amount of catalyst and pressure used and the temperature.

Diluents, such as dimethyl ether, may be used but they seem to offer no great advantage chemically. Small amounts of oxygenated compounds may be employed as promoters or components of the catalyst, as in the form of complexes.

In the broader, but not limiting conception, BF acts to cause alltylation of a central phosphorus atom by forming a ccmplex with the phosphite, thus making it readily susceptible to this alkylation. For example, boron trii'lucride forms a complex with dimethyl hydrogen phosphite, this complex then acting as a catalyst for further reaction. A product of this alkylation is the formation of a mono alkyl phosphite. When the diester is consumed to a point where its bimoleeular reaction is very slow, temperature promotes the alkylation of the phosphorus atom in the mono alkyl phosphite. Side and consecutive reactions such as the formation of phosphorous acid and its decomposition to phosphoric acid and phosphine derivatives are not catalyzed by BF although they proceed during the SP catalyzed reaction.

The separation of an intermediate reaction product into its components, i. e., dimethyl phosphite. dimethyl methane phosphonate and monomethyl phosphite may be accomplished by selective absorption, solvent extraction, extractive or azcotropic distillation. A favored method for obtaining pure dimethyl methane phosphonate involves first a vacuum distillation under about 10 mm. Hg, whereby this compound and unconverted feed are taken overhead. This distillate then may be subjected to extractive distillation under reduced pressure in the presence of a hydrocarbon or other suitable third component whereby it is recovered in the bottoms and removed in a pure state by stripping.

The invention is claimed as follows:

1. A catalyst which consists in a complex of dimethyl hydrogen phosphite with boron trifluoride.

2. A catalytic process for producing methane phosphcnic acid derivatives which comprises heating dimethyl hydrogen phosphite in the presence of BF catalyst at temperatures in the range of to 250 C.

3. A catalytic process of converting dimethyl hydrogen phosphite to dimethyl methane phosphonate, which comprises reacting the phosphite in the presence of a 131 catalyst at a temperature from about 160 to about 200 C.

4. A catalytic process of converting dimethyl methyl hydrogen phosphite to methane phosphonic acid and its derivatives which comprises reacting the phosphite in the presence of boron trifluoridc at about 160 to 200 C. until a substantial amount of the phosphite is converted to methane phosphonic acid derivatives, and heating the resulting mixture to a temperature above 220 C. until remaining phosphites in said mixture are converted to more of said methane phosphonic acid derivatives.

5. A catalyst for the alkylation of an organic phosphitc consisting in a mixture of dimethyl hydrogen phosphite and boron fluoride.

6. A process for preparing an alkyl phosphonic acid derivative of dimethyl hydrogen phosphite, which comprises mixing the phosphite with BF and heating the resulting mixture to a temperature of about 160 to about 250 C. until a substantial. amount of the phosphite is converted into phosphonate.

7. A catalytic process for producing phosphonic acid derivatives which comprises heating crude dimethyl hydrogen phosphite in the presence of BF to temperatures of about 160 to 250 C. until a substantial amount of the phosphitc is converted into phosphonate.

8. A catalytic process for converting an organic phosphite to phosphonates which comprises reacting dimethyl hydrogen phosphite in the presence of BP at a temperature from about 160 to about 200 C. until a substantial amount of the initial phosphite is converted to phosphonate and heating the resulting reaction mixture to a temperature above about 220 C.'unti1 remaining phosphites in said mixture are converted to phosphonate products.

9. A catalytic process of converting an organic phosphite to phosphonic acid and derivatives including phosphonates which comprises admixing dimethyl hydrogen phosphite and BF;, catalyst with hot phosphonic acid derivatives subsequently produced to form a reaction 10 mixture, heating the reaction mixture to a temperature above 220 C. until remaining phosphites are converted to form said hot phosphonic acid derivatives.

10. A process as described in claim 9, wherein BF; is first added to the phosphite which is then partly reacted therewith before admixing with the hot phosphonic acid derivatives.

References Cited in the file of this patent UNITED STATES PATENTS 2,397,422 Kos-olopoif Mar. 26, 1946 2,425,839 Schulze et a1. Aug. 19, 1947 2,436,141 Goebel Feb. 17, 1948 2,492,994 Harman et a1. Jan. 3, 1950 2,596,679 Hagemeyer May 13, 1952

Claims (2)

1. A CATALYST WHICH CONSISTS IN A COMPLEX OF DIMETHYL HYDROGEN PHOSPHITE WITH BORON TRIFLUORIDE.

2. A CATALYTIC PROCESS FOR PRODUCING METHANE PHOSPHONIC ACID DERIVATIVES WHICH COMPRISES HEATING DIMETHYL HYDROGEN PHOSPHITE IN THE PRESENCE OF BF2 CATALYST AT TEMPERATURE IN THE RANGE OF 160* TO 250*C.